Biomedical Engineering Reference
In-Depth Information
(A)
(B)
3
Measured ±SD
10
5
Ideal
2
0
Fluoro
5
1
10
15
20
Clear
0
0
5
10
15
20
25
30
35
( μ m )
y
500
550
600
650
Wavelength (nm)
(D)
(C)
x 10 -3
6
10
5
4
0
Fluoro
Clear
2
5
10
15
20
0
-2
0
5
Ideal
10
15
20
25
30
-4
Measured ±SD
35
500
550
600
650
3
-In ( σ Δ n ) (-)
4
5
6
7
Wavelength (nm)
Figure 14.11
(A) Negative log of the normalized spectrum from the center of each bead. (B) True color
representation of the sample superposed on the topological map. (C) Changes in the RI for a
point at the center of each bead. (D) Negative log of the standard deviation of the changes in the
real part of the RI superposed with the topological map. Source: From Ref. [60] .
The last step is to investigate the dispersive properties of these samples using NLDS. For
this analysis, recall that we have already obtained the residual phase,
Δφ
ω
), which
contains the cumulative dispersion from the system, background medium, and sample. In
order to isolate the sample-induced dispersion only, the average residual phase of a
background region is used as a reference to remove all dispersive contributions from
outside of the sample of interest. The resulting phase contribution is related to the changes
in the sample's RI by
(
Δn for locations
corresponding to the middle of the clear and fluorescent beads. For comparison,
Figure 14.11C also shows the ideal dispersion for the fluorescent bead, which is calculated
using a subtractive Kramers Kronig relation [65] , and agrees well with the measured
spectra. Additionally, Figure 14.11C indicates that the fluorescent bead exhibits much
greater amount of dispersion than the clear bead, a result anticipated by the principles of
causality.
Δφ
(
ω
)
5
(
ω
/ c 0 )2 dΔn (
ω
) [55] . Figure 14.11C shows
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